1. Field of the Invention
The invention relates to a process for the production of 2-hydroxypyridines, especially 2-hydroxypyridine carboxylic acid and 2-hydroxyalkyl pyridine.
2. Prior Art
2-hydroxypyridines can be obtained by diazotization of the corresponding amine pyridines and subsequent treatment with alkali lye. 2-hydroxypyridines can also be obtained from pyridine sulfonic acids or halogen pyridines by exchange with alkali, possibly by means of metal catalysts, such as, copper. The literature describes converting pyridine-N-oxide with acetic acid anhydride to 2-acetoxypyridine, which can be converted by hydrolysis into 2-hydroxypyridine or 2-pyridone. On the other hand, the reaction of picolinic acid-N-oxide with acetic acid anhydride only produces 2-hydroxypyridine in small quantities. Pyridine-N-oxide develops as the main product. [See J. Org. Chemistry, 26, (1961), 428.] Whenever the same reaction is carried out with isocinchomeronic acid-N-oxide, in an analogous manner only traces of 6-hydroxynicotinic acid are obtained and nicotinic acid-N-oxide is the main product. The reaction of 6-methylpicolinic acid-N-oxide, with acetic acid anhydride is an exception, which produces 2-hydroxy-6-methyl pyridine in a good yield. [See Bull. Chem. Soc. Japan 42, 3350, (1969).]